Adaptive thermogenesis — does it go away after weight maintenance? Original paper

As previously reviewed in Study Summaries, weight loss results in reductions in energy expenditure simply due to the reduction in body mass — a smaller body requires less energy. However, in some cases, this decrease in energy expenditure is greater than can be explained by the loss in body weight — a phenomenon known as adaptive thermogenesis.

The authors of this secondary analysis of another randomized controlled trial^[1] assessed whether adaptive thermogenesis remained significant after a period of weight maintenance. In addition, they assessed whether adaptive thermogenesis was related to changes in body composition, weight-related hormones, or the extent of energy restriction.

The investigators randomized 94 sedentary former elite athletes in Portugal with BMI ≥ 24.9 to a 12-month lifestyle intervention group or a waitlist control group. The participants in the lifestyle intervention underwent a 4-month weight-loss period, during which they aimed to reduce their calorie intake by 300–500 kcal per day under the guidance of a registered dietitian while attending weekly educational sessions designed to promote behavioral change. The participants then underwent an 8-month weight maintenance period, during which they continued to meet with a registered dietitian to adjust calorie intake as necessary to promote weight maintenance.

At baseline and after 4 and 12 months (after the weight-loss and weight-maintenance periods, respectively), the authors assessed the following outcomes:

• Body weight and BMI
• Fat mass, fat-free mass, and lean soft tissue, via DXA
• Measured resting energy expenditure (mREE), via indirect calorimetry
• Predicted resting energy expenditure (pREE), based on changes in fat mass and fat-free mass
• Physical activity energy expenditure (PAEE), via accelerometers
• Total daily energy expenditure, based on mREE, PAEE, and the thermic effect of food (assumed to be 10% of TDEE)
• Adaptive thermogenesis, defined as the difference between pREE and mREE
• True energy intake, based on observed changes in fat mass, fat-free mass, and energy expenditure
• Dietary adherence, by comparing true energy intake to prescribed energy intake
• Serum levels of thyroid stimulating hormone (TSH), free triiodothyronine (FT3), free thyroxine (FT4), insulin, and leptin

The participants in the intervention group lost 4.3 kg (approximately 9.5 pounds) during the weight-loss period and kept the weight off at the end of the study. Adaptive thermogenesis was significant after both 4 and 12 months — mREE was 85 kcal lower than pREE at 4 months and 72 kcal lower at 12 months.

Adaptive thermogenesis was associated with a larger energy deficit during the weight-loss period and with a greater loss of trunk fat mass at 12 months. It was not associated with total weight loss, hormonal markers, or dietary adherence.

A subanalysis comparing participants with adaptive thermogenesis (those with mREE lower than pREE) to participants who experienced the reverse (those with mREE higher than pREE) indicated that the participants with adaptive thermogenesis experienced less weight loss and fat loss and had a lower baseline energy intake.